Posts Tagged Trenberth

Climate change denier and Auckland University geographer Chris de Freitas seems to have fast access to the dialogue pages of the NZ Herald. His latest effort this week is a long ramble ostensibly around the possibility of an El Niño this year, but at its centre contains a nasty slur on the honesty of climate scientists. He confuses, presumably deliberately, predictions of a weather event in the short term with the longer term predictions of climate change.

The short term prediction relates to the possibility of an El Niño event this year. He claims NIWA’s reported 50% chance of an El Niño is not a prediction at all, but more akin to tossing a coin. This observation doesn’t stand up. NIWA doesn’t say every year that there’s a 50% chance of an El Niño. They were drawing attention to current developments which point in the direction of an El Niño.

Nevertheless de Freitas presumably sees his observation as a useful build-up to his planned attack. His next step is to comment on how incredibly complex climate systems are, and to quote no less an authority than Albert Einstein who said of the weather that prediction for even a few days ahead is impossible. Incidentally I’ve never seen a climate scientist claiming to predict the weather next week. But in de Freitas’ mind this leads to a climax:

The problem is complicated by the fact that the public usually fear the worst, and fear sells. So, if the period for which the prediction is made is beyond the end of the climate scientist’s lifetime, such as with long-term predictions of human-caused climate change, or “global warming”, any scary prediction will attract attention and hopefully also research funds or job promotion.

There follows a comment which perhaps is intended to qualify, but is vague and undeveloped and certainly does not undo the damaging assertion which precedes it:

Many experts passionately declare they believe future climate will be dramatically different due to human action. However, the challenge in climate science is correctly attributing cause.

He then returns to El Niño and after some reflection on how difficult it is to predict El Niño events advises preparedness to adapt to drought and flood. Without any recognition of irony he concludes:

The emphasis needs to be on dealing with the social, political and economic impediments that prevent effective flood-risk or drought-risk reduction.

The Herald has hosted a sloppy article which despicably insinuates that climate scientists are deliberately overstating the risks of climate change in order to attract attention and increase their funding and job prospects. It’s a familiar claim in the denial industry, but surely not one that our leading newspaper should allow in the face of the overwhelming scientific judgment that the the findings of climate science are authentic.

I can think of no journalistic standard to justify opening a responsible newspaper’s opinion pages to a propagandistic accusation which casually defames the integrity of thousands of climate scientists.

Gareth adds: NIWA’s stated probability of an El Niño event looks conservative, as the Herald article to which de Freitas responds points out. For a regularly updated outlook, I recommend the Australian Bureau of Meteorology’s web site here. BOM’s current expectation (issued on April 22nd) notes:

The likelihood of El Niño remains high, with all climate models surveyed by the Bureau now indicating El Niño is likely to occur in 2014. Six of the seven models suggest El Niño thresholds may be exceeded as early as July.

El Niño events are also associated with spikes in global temperature as ocean heat is released to the atmosphere and heat transfer to the deep ocean is slowed. The earlier this event gets going, the bigger the impact on this year’s temperatures will be, but it is likely that the biggest impact on global average temperature will be in 2015. Joe Romm has more on that at Climate Progress.

The IPCC released the summary for policymakers of its Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) in Kampala, Uganda, on Friday (SPM, SREX site, launch presentation slides). The report concludes that globally there has been a significant decrease in cold days and nights and an overall increase in warm days and nights, that it’s likely that “anthropogenic influences” have led to warming of extreme daily minimum and maximum temperatures, and that heavy rainfall events are increasing in many areas. There has also been an increase in extreme coastal high water events.

The report also projects that it is “virtually certain” that increases in the frequency and magnitude of warm daily temperature extremes will continue through this century, and that there will be corresponding decreases in cold extremes. It’s also very likely that heat waves and warm spells will become more frequent and warmer. Heavy rainfall events are also expected to increase, and the proportion of rain falling in those events is likely to increase. There are also likely to be more problems from storm surges and sea level rises, an increase in droughts, and landslides in mountainous regions.

Much of the report’s content will come as little surprise to those who have been following the subject — in common with previous IPCC reports the conclusions are conservative, couched in laboriously exact language, and exclude the most recent work1 — and for me the most interesting parts are the discussions of how extreme weather events interact with human populations to create disasters. In this respect, arguing about whether an event was “caused by” or “made worse by” warming is largely irrelevant to trying to find ways to reduce the impact of current and future extremes.

Meanwhile, the usual suspects are scrabbling around looking for ways to misrepresent the report’s findings. The most egregious to date comes from Nigel Lawson’s secretly-funded “Global Warming Policy Foundation”, who pick a paragraph out of context and pretend that it shows that…

According to a preliminary report released by the IPCC, there will be no detectable influence of mankind’s influence on the Earth’s weather systems for at least thirty years, and possibly not until the end of this century.

Al Gore didn’t hesitate to dwell on extreme weather events as evidence of the reality of climate change in his closing address for the 24-hour Climate Reality Project last week. There has certainly been no lack of them in the past year or so. Was he pushing the boundaries of the science? It wouldn’t worry me too much if he was because there’s plenty else in the scientific projections which is clearly under way, such as the melting polar ice or the acidification of the oceans. But Gore is a very intelligent and well-informed man and I don’t think he allowed himself to be carried away beyond the scientific mandate. Consider what is being said by some scientists right now.

“According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years.”

And the process is already under way:

“We also analyzed historical data from weather stations around the world to see if the projected emergence of unprecedented heat had already begun. It turns out that when we look back in time using temperature records, we find that this extreme heat emergence is occurring now, and that climate models represent the historical patterns remarkably well.”

This supports the projections:

“The fact that we’re already seeing these changes in historical weather observations, and that they match climate model simulations so closely, increases our confidence that our projections of permanent escalations in seasonal temperatures within the next few decades are well founded.”

Boston University researchers have published a paper (full text) in the current issue of Climatic Change Research. The lead author is Bruce Anderson, Associate Professor, Geography and Environment.The press release explains:

Anderson’s research indicates that if the 2°C increase [the current international target for limiting emissions] were to come to pass 70—80% of the land surface will experience summertime temperature values that exceed observed historical extremes (equivalent to the top 5% of summertime temperatures experienced during the second half of the 20th century) in at least half of all years. In other words, even if an increase in the global mean temperature is limited to 2°C, current historical extreme values will still effectively become the norm for 70-80% of the earth’s land surface.

Anderson comments:

’Many regions of the globe–including much of Africa, the southeastern and central portions of Asia, Indonesia, and the Amazon–are already committed to reaching this point, given current amounts of heat-trapping gases in the atmosphere.’

In the United States, the impacts are expected to be most severe over the western third of the country. ’In these regions, if the 2°C threshold is passed, it is more likely than not that every summer will be an extreme summer compared with today.’

’While previous work, including our own and that of researchers at Stanford, has highlighted that summertime temperature extremes, and how frequently they occur, will change significantly even in response to relatively small increases in global-mean temperatures, the extent and immediacy of the results really caught us off guard. Because these results are referenced to increases in global-mean temperatures, and not some particular time or change in amount of heat-trapping gases, they hold whether we reach this global-mean temperature increase in the next 40-50 years as currently projected, or the next century. They really are telling us that this is a temperature threshold that poses significant risks to our lives and livelihoods.’

Climate Communication is a new group set up to combine expertise in climate science with clear and accessible communication to the public. They have recently published an article setting out very clearly the connections scientists see between recent extreme weather events and climate change. The expert science reviewers are Kevin Trenberth and Jerry Meehl, National Centre for Atmospheric Research, Jeff Masters, Weather Underground and Richard Somerville, Scripps Institution of Oceanography, University of California, San Diego. Here are one or two extracts from the overview:

As the climate has warmed, some types of extreme weather have become more frequent and severe in recent decades, with increases in extreme heat, intense precipitation, and drought. Heat waves are longer and hotter. Heavy rains and flooding are more frequent. In a wide swing between extremes, drought, too, is more intense and more widespread…

Small changes in the averages of many key climate variables can correspond to large changes in weather. Substantial changes in the frequency and intensity of extreme events can result from a relatively small shift in the average of a distribution of temperatures, precipitation, or other climate variables…

In contrast, the observed trends fit well with our understanding of how climate change drives changes in weather. Computer models of the climate that include both natural forces as well as human influences are consistent with observed global trends in heat waves, warm days and nights, and frost days over the last four decades. Human influence has also been shown to have contributed to the increase of heavy precipitation over the Northern Hemisphere.

The article covers several aspects of the subject in the course of its 28 pages — precipitation patterns, floods, droughts, heat waves, hurricanes, winter storms and more. All is unobtrusively but carefully referenced to scientific papers and reports. It is fully accessible reading for the non-scientist and betokens a valuable role for Climate Communication.

The conclusion of the article:

Human-induced climate change has contributed to changing patterns of extreme weather across the globe, from longer and hotter heat waves to heavier rains. From a broad perspective, all weather events are now connected to climate change. While natural variability continues to play a key role in extreme weather, climate change has shifted the odds and changed the natural limits, making certain types of extreme weather more frequent and more intense.

While our understanding of how climate change affects extreme weather is still developing, evidence suggests that extreme weather may be affected even more than anticipated. Extreme weather is on the rise, and the indications are that it will continue to increase, in both predictable and unpredictable ways.

So no, Al Gore did not overstep the mark. He simply expressed with urgency the reality that we are indeed causing more extreme weather events by continuing to increase the level of greenhouse gases in the atmosphere.

Here it is straight from the scientists in the Climate Communication article:

Late notice, for which I apologise, but climate scientist Kevin Trenberth is giving a public lecture in Wellington on Friday (July 15th) on The Russian heatwave and other recent climate extremes. Trenberth’s talk is being organised by the NZ Climate Change Research Institute and will be at the Old Government Buildings Lecture Theatre 2, from 12:30 — 1:30pm. If you can’t make it, you can get a good idea of what he will discuss from this guest article by KT posted at Skeptical Science this week. Well worth a read. Trenberth is also holding a media briefing for the Science Media Centre tomorrow afternoon, which I hope to report on in due course.

Also this week, the Saunders, Oram and Salinger road show has added an extra gig into their Northland tour — in Dargaville tomorrow at 1-30 pm at the Kaipara District Council, 42 Hokianga Road, Dargaville. Contact email protected for more information. Jim S also asks me to note that the title of the urban talks ( in Timaru, Auckland and Dunedin) has changed to Preparing for White Swans: Climate change and opportunities for the economy. Full tour details here (pdf).

The CCRI has just released the July edition of their What’s Hot newsletter, full of recent climate related news, linked to the original articles. It’s a good digest of recent news, worth the download.

I listened with interest to Kevin Trenberth on the latest Climate Show describing how the increased water vapour in the atmosphere resulting from human-caused global warming is leading to greater extremes in weather events. It sent me back to take another look at the section in James Hansen’s book Storms of My Grandchildren where he explains the greatly increased strength of storms we can expect as the century unfolds, unless we leave most fossil carbon in the ground. I reviewed the book a while back on Hot Topic and thought it worth outlining more closely here, as an extension of my review, Hansen’s argument in the ten pages where he specifically addresses the storms of which the book’s title speaks.

As ice sheet disintegration begins in earnest he writes of a chaotic transition period in which our grandchildren will live the rest of their lives. Ice sheet disintegration in Earth’s past needed millennia, but human forcing is so much more powerful than natural forcings that ice sheets will respond much more rapidly. Currently most of the recent energy imbalance due to increased greenhouse gases in the atmosphere is warming the ocean and only a small fraction is being used to melt ice. This division of excess energy will shift more to ice melt as the ice sheets are softened up and begin to discharge ice to the ocean more rapidly.

Increased ice discharge in both West Antarctica and Greenland will cool the neighbouring ocean. Although Greenland is not as vulnerable to rapid collapse as West Antarctica is it can lose mass fast enough to influence North Atlantic Ocean surface temperature. This freshwater melt will also decrease the salinity and hence the density of the water, making it less able to sink to the ocean bottom as it currently does, where it feeds the ocean ’conveyor’ circulation and allows warmer water to move north to replace it. If that deepwater formation slows down the regional North Atlantic cooling from ice melt will be enhanced.

Meanwhile in low latitudes the atmosphere and the ocean surface will be getting warmer and warmer as the century proceeds. This will exacerbate trends already apparent such as mountain glacier melting, expansion of dry sub-tropical regions, more intense forest fires and competition for diminishing freshwater supplies. There will be increased desiccation but in other times and places heavier rain and increased floods.

The greatest impact warming will have on storms is through the increase in water vapour it causes. Atmospheric water vapour increases rapidly with only a small temperature rise. Latent heat is the energy acquired by water vapour when it evaporates. When it condenses that latent energy is released as heat that is potentially available to fuel a storm. The storm types driven by latent heat include thunderstorms, tornadoes, and tropical storms such as hurricanes and typhoons. The greater availability of this heat will mean that the strength of the strongest storms will increase as global warming increases. There will also be an expansion of the regions liable to severe storms.

This is just the beginning. There are three ratcheting effects in waiting. One is the development of more powerful and destructive mid-latitude or frontal cyclones. They depend on the temperature difference between the cold and warm air masses as well as on the amount of moisture in the atmosphere behind the warm front. The melting ice sheets will exacerbate this once they begin to disintegrate rapidly enough to keep regional ocean surface temperature from rising as fast as continental temperatures and temperatures at lower latitudes. Increased moisture content in lower- and mid-latitude warm air co-existing with ice-cooled polar air masses will increase the intensity of frontal cyclones.

The consequences of even a metre of sea level rise combined with increased storm strength are horrendous to contemplate.

The second ratcheting is far greater. It occurs when the ice sheets’ rapid disintegration causes a sea level rise measured in metres. Eventually ice sheets begin to disintegrate at rates of several metres of sea level rise per century. We could soon create conditions that guarantee this happening, but it is likely to be several decades before a rapid sea level rise begins. Hansen notes that we have been surprised by how fast some other climate changes have occurred, but for the moment offers his best estimate of when large sea level change will begin as during the lifetime of his grandchildren. The consequences of even a metre of sea level rise combined with increased storm strength are horrendous to contemplate. He offers a few examples of what it will mean for vulnerable places in various parts of the world.

The third ratcheting effect would be the melting of methane hydrates. Of greatest concern are those in sediments on the ocean floor, because of their great volume. Hansen relates the chance of their melting to possible ocean circulation changes because of the freshwater additions to both the North Atlantic and Antarctic Oceans through ice sheet disintegration. Global ocean circulation reorganised during the Paleocene-Eocene thermal maximum about 54 million years ago when a sudden large global warming occurred and deep water formation took place in the Pacific rather than the North Atlantic, flooding the ocean floor with warmer Pacific Ocean water. If that happens again, melting methane hydrates, there will be no plausible way for humans to reverse the change of ocean circulation. The released methane added to the high levels of carbon dioxide will result in a huge planetary energy imbalance and the remaining ice on the planet will disappear. That means a sea level rise of 75 metres.

Hansen, as usual, communicates the science to his readership with clarity and fully appropriate urgency. These are not remote consequences he is exploring, but at least strong possibilities and in some cases inescapable certainties. No lay reader prepared to take a little time to come to terms with the concepts can fail to understand the serious risks we run if we carry on exploiting fossil fuels. No policy maker can claim not to have been made aware of the danger of continuing on our present course.

Hansen is not off on some flight of fancy of his own. He is interpreting solid mainstream science. It’s from that base that he says towards the end of the book that our planet is in imminent danger of crashing and that the fight for effective policies to prevent that is the most urgent fight of our lives.

The Climate Show returns with a packed show, featuring one of the world’s best known climate scientists, NZ-born, Colorado-based Dr Kevin Trenberth — star of the Climategate “where’s the missing heat” emails. He’s been in New Zealand to visit family (experiencing the Christchurch quake in the process) and to attend a conference, and his comments on the state of our understanding of climate change should not be missed. John Cook of Skeptical Science returns with his new short urls and an explanation of why declines have never been hidden, and Gareth and Glenn muse on Arnie “Governator” Schwarzenegger riding to the rescue of climate science, cryospheric forcing and carbon cycle feedbacks from melting permafrost, and a new paper that suggests that current policies are pointing us towards extremely dangerous climate change. All that and hyperbranched aminosilica too…

Watch The Climate Show on our Youtube channel, subscribe to the podcast via iTunes, or listen direct/download here:

Christchurch earthquake, Feb 22 2011. At the time of writing the death toll was expected to rise to over 240. At least 100 of those who died were tourists or foreign students. If you would like to donate to support the recovery effort, please consider the Red Cross appeal.

Feature interview:: Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research in Boulder Colorado. Born in NZ, worked at MetService, now based in Colorado, one of the highest profile climate scientists in the world, and a regular subject of attacks by denialists. The AMS paper referenced is available from KT’s web site linked above.

It’s a grim day in Canterbury. 75 people are confirmed dead and 300 are missing following the magnitude 6.3 earthquake which struck at 12-51pm yesterday. As I write, teams of urban search and rescue specialists from NZ and Australia (soon to be joined by teams from all over the world) are crawling over collapsed buildings throughout the central city. The cathedral (above) has lost its spire, and there are bodies in the rubble around it. I am glad to report that my family and friends, and that of Climate Show co-host Glenn Williams are well, but no-one is untouched by this terrible disaster. Up here in Waipara the initial shaking was bad enough to make us run outdoors, but our relief at escaping damage was immediately tempered by the realisation that someone had just taken a hammering…

For an inkling of the scale of this tragedy and its impact on people who had already survived a magnitude 7.1, but much less damaging, quake last September, I commend author David Haywood’s eloquent description in the Guardian, and Press journalist Vicki Anderson’s heartfelt story of her escape from the Press building (under the cranes in the picture above). US-based NZ climate scientist Kevin Trenberth was also in town, holidaying with his family. This is his account:

Where we were [hillside suburb of Mt Pleasant] was actually the epicentre of the earthquake, which occurred at 9 minutes to 1p.m. We immediately got under the dining room table. The quake was very sharp and the whole ground bucked and heaved. It was very shallow and the devastation was immediate. Everything came off the walls, the china cabinet and all the crystal, nearby crashed around us. In the kitchen, 2m away, the cupboards emptied, the built-in wall oven crashed onto the floor followed by the built-in microwave. Then the big refrigerator with bottom freezer fell on top of all that. Broken glass everywhere. In the room we were in, there were 6 mm plate glass windows that were smashed, and likewise in the adjacent living room. But the house held in front. Not so in the back. The back wall was bricked and had a French door: the wall collapsed and the door jerked out and away from the house so it is wide open (and thus open to looters). The adjacent walls were half brick and they too were wiped out.

Banks of rocks and solid ground near the house collapsed and made it difficult to get out. The road outside had a big crack and the sidewalk dropped 20 cm relative to the road and a gap opened 8 cm wide. The water main broke just above there and water cascaded down past the front of the house, making it a wet experience getting to my rental car, which was OK.

Trenberth spent today in Christchurch helping the rescue effort, along with many, many others. You can get some idea of the size of this event by looking at aerial pictures taken by the NZ defence forces: aside from the building damage in the central city, extensive damage has occurred in many suburbs and soil liquefaction and flooding is affecting tens of thousands of homes. Power is out in 50 per cent of the city, and the mayor has described the water and sewer systems as “trashed”. Recovery is going to take a very long time, but recover and rebuild we will.

I would urge anyone with spare cash to make a donation to the various appeals that are running — there’s a full list here, and the NZ Red Cross is calling for donations (link was down at time of writing). [Update: see NZ based donation service at bottom of article -- 100% of monies will go to ChCh mayoral fund.]

Earth science geeks will want to check out the Christchurch Quake Map here (link takes you to last seven days — use the drop down to select Feb 22) for a remarkable visualisation of the earthquake sequence we’ve been experiencing, and the Highly Allochthonous blog has an excellent description of the tectonics of the quake here. It also worth noting that the quake caused a major calving event on the Tasman Glacier lake near Mt Cook. An estimated 30 million tons of ice broke off the glacier tongue when the quake hit.

I hope that Hot Topic readers will understand if my contributions to the site are somewhat disrupted over coming weeks. My focus will be elsewhere, and at the moment it’s very difficult to take the future for granted. A lesson for us all there, perhaps?

Update: this amazing picture of the clouds of dust rising from the city moments after the quake hit looks to have been taken from one of the hill suburbs. Hat tip to @georgedarroch on Twitter, photographer unknown*. Click for full size.

The last few weeks have seen some extraordinary weather events around the world: relentless extreme heat in Russia, biblical flooding in Pakistan and devastating landslides in China. Tens of millions of people have had their lives disrupted and thousands have died, and — beyond reasonable doubt — global warming is playing a part in creating these extremes. But how much of a part? Michael Tobis asked this question in a recent post:

Are the current events in Russia “because of” “global warming”? To put the question in slightly more formal terms, are we now looking at something that is no longer a “loading the dice” situation but is a “this would, practically certainly, not have happened without human interference” situation?

The answer, at least in the case of the current extremes, would appear to be yes.

Jeff Masters at Weather Underground has (as usual) been providing exemplary coverage of the Russian heat wave, and in a post on August 6th he described it as “one of the most remarkable weather events of my lifetime”. Over the month of July, Moscow’s mean daily temperature was 7.8ºC above normal (the previous record, set in 1938, was 5.3ºC above normal), and since the beginning of August the daily maximum has been consistently 15ºC above average, which Masters describes as “a truly extraordinary anomaly”. At the time of writing, Moscow had experienced 29 successive days with temperatures over 30ºC, easily the longest and most intense heat wave since records began. Masters quotes Alexander Frolov, head of Russia’s weather service:

Our ancestors haven’t observed or registered a heat like that within 1,000 years. This phenomenon is absolutely unique.

What’s particularly striking about this event is the large margin by which previous long-standing records are being smashed. The Economist, in an excellent article on climate change and extreme weather, quotes Dutch meteorologist Geert Jan van Oldenborgh on the odds:

…a straightforward comparison of the temperatures seen this summer with those of the past 60 years suggests that a large patch of Russia is experiencing temperatures which might be expected only once every 400 years or so. Some places within that patch are hotter than might be expected over several millennia.

…the heatwave starts to look less improbable–more like the sort of thing you might expect every century. As the warming trend continues in the future, the chances of such events being repeated more frequently will get higher.

Van Oldenborgh did a similar analysis of the heat and cold anomalies of last northern hemisphere winter, which I covered back in April. The key point is that if the climate were not changing, an event as dramatic as the Russian heatwave would be very, very unlikely. If we factor in the warming trend, it remains unusual, but less so. And if that warming trend continues (and it will), then we can expect more record-breaking heat waves around the world.

Global warming impacts the weather we experience in two ways: by increasing the probability of new records — when a heat wave happens, you are likely to get more warmth (see the graph in my post on rainfall). But there is a second impact: the potential for changes in the circulation of the atmosphere. The climate of any part of the planet depends on lots of factors, but the flow of weather systems is crucial. As an example, consider the South Island of New Zealand. The prevailing (or normal) wind is westerly, and when that wind bumps into the Southern Alps it drops rain, and lots of it. Hence rainforest, speedy glaciers and tourism. On the other side of the Alps, we get warm dry winds and little rain. Now imagine that the frequency of easterly winds increases and westerlies decrease. The east coast gets wetter, and the west coast dryer. Cue big change in climate, even if the temperature doesn’t warm. There’s actually a hint of this happening in the modelling toward the end of the century — though for the east coast of the north island, not down here.

So can we draw a line between Russian heat, flooding in Pakistan and China and changes in the pattern or shape of weather? Perhaps a combination of the after-effects of El NiÃ±o, record sea-surface temperatures in the tropical Atlantic and a reduction in Arctic sea ice are affecting the way the jet stream meanders around the northern hemisphere, creating a persistent ridge of high pressure over Russia — a blocking pattern that has flow on effects for Asia. Wiredasked Kevin Trenberth if the heat and floods could be linked:

’The two things are connected on a very large scale, through what we call an overturning or monsoonal circulation,’ he said. ’There is a monsoon where upwards motion is being fed by the very moist air that’s going onshore, and there are exceptionally heavy rains. That drives rising air. That air has to come down somewhere. Some of it comes down over the north.’

Rob Carver at Weather Underground explains more here, New Scientist discusses the “frozen” jet stream here and UK Met Office scientist Peter Stott (who wrote the definitive paper on the record-breaking European heat wave of 2003) offers his thoughts at the Guardian.

What I find scary in all this is the multiple coincidence of record heat and catastrophic flooding in Pakistan and China — in a year where the first six months had already set a record for insurance losses on extreme events. The last 12 months have been the warmest in the global record. A modest El NiÃ±o event has boosted temperatures and affected weather patterns in an eery echo of events that followed the great El NiÃ±o of 1997-98. Back in 1999, Kevin Trenberth reviewed the extreme weather events of 1997-98. It was, as he suggests, a wild ride:

In early August, for example, major floods devastated parts of Korea, and in August and September 1998, extensive monsoon-related flooding struck heavily-populated eastern India and Bangladesh. Widespread heavy rains in China, at about the same time, released the mighty Yangtze River from its banks, with ensuing reports of more than 3,000 deaths, some 230 million people homeless, and over $30 billion in flood damage. In the summer of 1998 heat waves and air pollution episodes plagued many regions of the world, particularly in Egypt and other Mediterranean countries, and in southern Europe. In New Zealand, record floods in July and October 1998 were the worst in 100 years. But the costliest disaster of them all, in terms of human life, struck the Caribbean in late October. Hurricane Mitch caused the deaths of more than 11,000 people in Honduras, Nicaragua, Guatemala and El Salvador, primarily through the extensive flooding that followed prolonged and heavy rains.

This time round the floods are in Pakistan instead of India and Bangladesh, and the heat has moved north from the Mediterranean to Russia. The Atlantic hurricane season has not yet really got going, but we can only hope there won’t be another Mitch. In the 12 years since that El NiÃ±o, the climate system has continued to accumulate energy. When an ENSO event releases that energy it has to go somewhere, and that’s into heatwaves, floods, hurricanes and melting ice.

As the years go by and the warming continues, those extremes are only going to get worse. To me, it looks very much as though it won’t be a gradual warming that causes us the biggest problems, it’ll be the direct and indirect effects of increasing weather extremes. Hot years are going to be hard years for humanity.

I agree with Michael Tobis’s take at Only In It For the Gold that something systematic has changed to alter the global circulation and you’ll need a coupled atmosphere/ocean global model to understand what’s going on. My hunch is that a warming Arctic combined with sea-surface-temperature teleconnections altered the global circulation such that a blocking ridge formed over western Russia leading to the unprecedented drought/heat wave conditions. Without contributions from anthropogenic climate change, I don’t think this event would have reached such extremes or even happened at all.

The upshot: Whether with temperatures, precipitation, or storms (tropical or otherwise), and regardless of in which direction the extremes are, it's a case of Weather Gone Wiggy, and this is happening at the time when the Earth's climate is at an exceptionally warm level compared to that of at least the past century. There have been extremes for as long as there has been weather; it's their nature which is changing along with changing atmospheric moisture, stability, and circulation patterns.

And a plug: Jim Renwick is giving a talk on climate change at the Hurunui Library (yes, the one in the heat pump ads) in Amberley on Monday, July 5th at 7-30pm. All welcome. I’ll be heckling from the cheap seats…

The extreme weather flavour of the moment is without doubt heavy rain and flooding. As I write, severe flooding has caused 132 deaths in southern China and 19 in Burma. The Var region in southern France is recovering from spectacular flash flooding that killed 25 people (watch the BBC video), Tennessee’s recovering from a 1000 year flood in May, and NZ hasn’t escaped. The Metservice blog reports that the flooding in Whakatane a few weeks ago was caused by rainfall of 89.8mm in one hour (with more heavy rain either side of that hour). As the blog notes, that’s tropical rain happening well outside the tropics. But what struck me at the time was a comment from a Whakatane resident included in the TV3 News coverage of that flooding. I can’t remember his precise words, but it was something along the lines of “should be a wake-up call for anyone who doesn’t think global warming’s an issue, because this is what global warming delivers…” Perceptive, I thought, because one of the more robust predictions of climate science is sometimes described as an intensification of the hydrological cycle.

It works like this. Increasing CO2 in the atmosphere warms the planet. As the oceans warm up, more water vapour enters the atmosphere, and because it is itself a heat-trapping gas this adds to the warming. This positive feedback is important because it increases the amount of warming triggered by the CO2, but it’s also important because of impacts of the increase in water vapour itself. The increase has been measured: there’s about 4% more water vapour in the atmosphere now than there was 30 years ago, and I suspect that we’re now seeing the effects of that on our day to day weather.

Water vapour is sometimes described by meteorologists as the “fuel” that drives storms. As water evaporates from a warm ocean, it cools the surface and transfers energy into the atmosphere. As the water vapour condenses into clouds and rain, that energy is released, intensifying the storm. More water vapour, stronger storms, heavier rainfall.

4% extra water vapour doesn’t sound like a lot, does it? But it’s enough to change the probabilities of heavy rainfall events in two ways. Firstly, the frequency of heavy rainfall events will increase, and secondly the amount of rain that falls in the heaviest events will increase. Take a look at this graph (from NASA’s Earth Observatory feature on the costs of climate change):

The graph considers temperature extremes, but the same principle applies to rainfall (except that the probability distribution is pegged at zero — no rain). The top curve shows what happens if the climate warms but the variance — the size of the swings between warm and cold — remain the same. The middle curve shows a stationary climate (ie, not warming or cooling) but with a variance increase — more dramatic swings between hot and cold, but no new records. The effect is to squash the curve and create more warm and cold events. Combine the two, and you get increases in both the hot weather and in record heat. This is already being seen with heatwaves in Australia, for instance, and I suspect we’re now seeing the same effect happening with rainfall.

Joe Romm at Climate Progress has been diligently pursuing the issue of weather extremes as a symptom of climate change, and last week interviewed NZ scientist Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research in Boulder, Colorado, on the subject. It’s worth reading the full interview, and following the references, but here’s Trenberth making an important point. Romm asks about the best way to describe the increasing extremes:

I find it systematically tends to get underplayed and it often gets underplayed by my fellow scientists. Because one of the opening statements, which I’m sure you’ve probably heard is ’Well you can’t attribute a single event to climate change.’ But there is a systematic influence on all of these weather events nowadays because of the fact that there is this extra water vapour lurking around in the atmosphere than there used to be say 30 years ago. It’s about a 4% extra amount, it invigorates the storms, it provides plenty of moisture for these storms and it’s unfortunate that the public is not associating these with the fact that this is one manifestation of climate change. And the prospects are that these kinds of things will only get bigger and worse in the future.

Earlier in Romm’s interview Trenberth had drawn attention to research that demonstrated that in the US, “the really heavy rainfall events – the top 1% and the top 0.3% – had gone up at even more alarming levels something like 27% as I recall over the last 30 or 40 years [actually 1967 to 2006].” Ring any bells? Jeff Masters comments and amplifies the point here. Then try a Google News search for the term “flood“, and see what pops up.

From my personal perspective, sitting in a farmhouse in North Canterbury on the east coast of the South Island of New Zealand, deep down in the South Pacific ocean, I think we’re seeing this effect quite clearly. I haven’t crunched the numbers for New Zealand, but I think they might show the same thing as the research Trenberth quotes. I’ve pondered the subject before, when considering the evidence of my rain gauge in 2008 and the climatic swings of 2009, but I can’t help but feel that as we head into the second half of a year that might set another global temperature record, we’re already seeing the concomitant impacts of increased water vapour in the atmosphere in the dramatic flood events happening around the world.

The lesson: climate change is not an abstract thing, a problem reserved for the future. It’s not only a slow but steady increase in long term averages, it’s also a change in the probability of extreme events, which are themselves becoming more extreme. The impact of climate change will be delivered by changes in the weather that we experience — and those changes are already happening. Worse, when the weather’s bad, it can and will be very bad indeed.

[Update 23/6: The Guardianreports on a new paper which suggests intensification of the hydrological cycle will persist, due to the thermal inertia of the global ocean, for a considerable period after CO2 levels have stabilised and been reduced. And Nature Newsdiscusses the terrifying power of flash flooding...]

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